1. Technical Field of the Invention
The present invention relates to a compressor and an electric motor suitable for same.
2. Description of Related Art
Conventional compressor is unduly heavy for its bulk. This is attributed to an electric motor incorporated therein accounting for one-third to half of the entire system by weight. An electric motor having an unduly large weight is practically undesirable regardless of its uses. However, to date little attention has been paid to weight reduction and no improvements have been made to eliminate such inconvenience.
The present invention has been devised in view of the above-described problem, and it is an object of the invention to provide a light-weight compressor and an electric motor suitable for the compressor.
To achieve the above object, according to a first aspect of the present invention, a compressor includes an electric motor operating on lower voltages, in which at least the winding of the stator is formed from a light-metal conductor wire having a specific gravity smaller than that of a copper wire.
In this construction, the weight of the entire compressor decreases substantially in proportion to the total volume of the windings. This is because, while the light-metal conductor wire differs from a copper wire in the value of electric resistance and accordingly in the range of effective sectional area properly set for handling lower voltages, it has a specific gravity smaller than that of a copper wire.
Here, using an aluminum wire makes it possible to realize a soft winding and thus facilitates the winding operation and subsequent re-forming operation, as compared with a copper wire. This also helps increase the slot space rate. Further, using a Litz wire as the light-metal wire is particularly preferable in a case where a larger wire diameter is required for the low-voltage electric motor, because the skin effect is less significant.
In a compressor according to a second aspect of the present invention, in order to achieve weight reduction, at least one of the stator and the rotor included in the electric motor has at least one of a cavity, a notch axially arranged continuously or discontinuously, and a hole formed on its surface in the circumferential direction.
In this construction, since the stator and the rotor have a lamination structure, the cavity, notch, or hole is formed with ease from a group of holes drilled in the laminated plate material, of which the cavity may be formed so as to lie scattered therearound as desired. The cavity, notch, and hole are essentially different than a cooling hole formed in the stator or rotor of a conventional compressor designed for a refrigeration cycle. The latter is formed for the purpose of cooling the electric motor by passing a refrigerant therethrough. That is, the former can be made as large as possible in size and number insofar as strength, safety, electric motor efficiency, and other factors concerning the compressor are maintained at adequate levels. The weight of the entire compressor decreases in proportion to the total volume of the cavity, notch, or hole.
In a compressor according to a third aspect of the present invention, at least one of the stator and the rotor included in the electric motor has one of a notch and a hole formed on its surface in the circumferential direction. The notch or hole acts as an axial sound deadening path for conveying a refrigerant.
In this construction, the axial notch or hole can be made larger in size and number than a conventional cooling hole. This makes it possible to reduce the weight of the compressor to a minimum. Simultaneously, this helps increase the passage area of the sound deadening path and thus obtain sufficient refrigerant noise suppression effect.
The sound deadening path may preferably be realized as a path extending forwardly only partway and having its opening in the refrigerant admission direction, as a path which is so shaped that its width decreases gradually from its refrigerant-admission side to its refrigerant-discharge side, or as a through path having an expansion chamber partway along its length. A sound deadening path thus designed exerts interference- or expansion-based excellent noise suppression characteristics.
In a compressor according to a fourth aspect of the present invention, an iron-based stator is bolted to a stepped surface of the inner periphery of an aluminum housing at three positions around its outer periphery.
This construction requires one fewer bolted positions in contrast to conventional cases where a stator needs to be bolted to a housing at four positions because it cannot be shrinkage-fitted thereto for reasons of material of the housing and the stator. This helps reduce the number of bolts and thick-walled portions necessary for bolting. This in turn helps reduce the weight of the entire compressor, as well as the number of constituent components and assembly man-hours, thereby achieving cost reduction.
Moreover, where the winding of the stator is formed from a star-shaped three-phase winding, it may preferably be wound in parallel. This makes it possible to create three boundary portions for the winding groups arranged along the circumferentially outermost portion of the stator. Then, by arranging the above-described bolted positions so that they face their corresponding boundary portions, any possible mutual interference of the winding groups can be avoided. Thus, there is no need for the bolted portions to protrude greatly outward to avoid such interference. This makes the stator smaller and thus helps reduce the weight of the electric motor.
In a compressor according to a fifth aspect of the present invention, the electric motor has an iron-based stator cast in the inner periphery of an aluminum housing.
In this way, the need for a bolt and a thick-walled portion necessary for bolting is eliminated, thereby leading to a reduction in the weight of the entire compressor. Simultaneously, this helps reduce the number of constituent components and assembly man-hours, thereby achieving cost reduction.
Any of the above-described compressors employs, as a power source, a battery which is moved concomitantly therewith, and has an electric motor and a compression mechanism driven by the electric motor housed in a housing. Such a construction is suitable for use as an air-conditioning mechanism in vehicles ranging up to large-sized passenger cars.